This patent refers to a tower crane with composite structure, self-assembling, with folding and then telescoping tower, and arm made up of several folding and unfolding sections.
Cranes are already known which have a self-assembling composite structure in which the vertical element, known as xe2x80x9ctowerxe2x80x9d, is composed of a pair of structural sections hinged together, and the horizontal element, known as xe2x80x9carmxe2x80x9d, is similarly composed of one or more sections hinged together. The sections of the vertical element are, when the crane is down, horizontal and laid down one on top of the other, while with the crane assembled they are vertical and in line with each other so as to form the crane""s tower. The sections of the horizontal element are likewise, when the crane is in the down position, horizontal and folded upon each other, and on top of the sections of the vertical element, while when the crane is assembled they are horizontal and in line with each other to form the arm of the crane.
There are various systems for passing from the position where the crane is down and the tower and arm sections are folded and horizontal to that in which the crane is assembled, with the tower sections in line and vertical and the arm sections in line and horizontal; the maximum height that the tower""s upper end, and consequently the arm attached to that end, can reach is in any case equal to the maximum length of the two tower sections hinged together.
This limits the use of a crane constructed in this way, since there is no way of reaching heights greater than the sum of the lengths of the tower sections. At the same time, considerations of transporting the disassembled crane prevent the arm sections being much longer than the tower sections, while the cumulative total height of the tower sections and arm sections laid one upon the other cannot, in view of the same considerations, exceed a certain height, thus limiting the number or height of the individual arm sections to be placed one upon the other.
In the case of cranes already known, the raising of the arm into its working position from its position with the crane down is carried out during the stage of lining up and erecting of the tower by means of a suitable relay of struts and tie rods; this generates considerable bending forces in the two tower sections and in the various types of component that may be used for erection of the tower. Furthermore, in known cranes at least one of the hydraulic actuators, preferably installed for the deployment and folding of the crane and of the arm, has a structural function in the deployed machine and cannot, therefore, be replaced in the event of failure while the crane is assembled.
One purpose of the present invention is therefore to create a crane with a self-assembling foldable and telescoping tower and a multi-section arm, to avoid the above-described technical problems.
Another purpose of the present invention is to create a crane of the above type which is particularly simplified in structure and construction, and which would be equally simple and effective in use.
Yet another purpose is to create a crane capable of performing the tasks required of it while still being particularly simple to use.
These purposes have been achieved in this invention with the creation of a crane with a self-assembling foldable and telescoping tower and multi-section arm as set out in the attached claim 1.
Further salient particular characteristics of this invention are covered by the dependent claims.
In particular, the crane in the present invention has a tower of composite structure made of at least one pair of hinged sections consisting of structural members, box girders of square or rectangular cross-section, and a third section inserted into the upper section of the hinged pair, this third section being composed of a single structural member or box girder of square or rectangular cross-section which can be telescoped once the two hinged sections are vertical and lined up, so that the upper end of the tower so formed can reach a greater height than that reachable by the hinged pair of sections alone. Furthermore, the particular small height of the individual arm sections allows a sufficient number of them to be placed one upon the other, when the crane is folded, for the arm to be of considerable length, and longer than can be achieved with other known cranes of the same type, when the crane is assembled.
Furthermore, since in the case of the crane created by this invention the telescoping of the third tower section takes place after the alignment in the vertical position of the pair of hinged sections, and it is only at that stage of telescoping that the arm is raised to its working height, progress is made towards the aim of reducing the bending stresses in the two hinged tower sections and the components used for erecting the tower.